System and Method for Terminal Cooperation Based on Sparse Multi-Dimensional Spreading

ABSTRACT

System and method embodiments are provided to achieve efficient Direct Mobile Communications (DMC) and device-to-device (D 2 D) communications for terminal based groups with improved spectrum efficiency, reduced interference, and virtual full duplex operation mode. The embodiments include a distributed mechanism for D 2 D communications that enables one or more cooperating UEs (CUEs) to help one or more target UEs (TUEs) with limited additional signaling overhead and relatively simple implementation. The mechanism comprises a grantless multi-dimensional multiplexing scheme that uses low density spreading (LDS) over time, frequency, and/or space domains to enable data forwarding between multiple half-duplex terminals or UEs while allowing the UEs to operate in virtual full-duplex mode.

This application is a continuation of U.S. Non-Provisional ApplicationSer. No. 13/862,168, filed on Apr. 12, 2013, and entitled “System andMethod for Terminal Cooperation Based on Sparse Multi-DimensionalSpreading,” which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/791,830, filed on Mar. 15, 2013, and entitled“System and Method for Terminal Cooperation Based on SparseMulti-Dimensional Spreading,” and U.S. Provisional Patent ApplicationSer. No. 61/737,643 filed on Dec. 14, 2012, and entitled “System andMethod for Direct Mobile Communications (DMC) Based on Two-DimensionalLow Density Spreading,” all of which applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the field of wireless communications,and, in particular embodiments, to a system and method fordevice-to-device (D2D) communications based on two-dimensional lowdensity spreading.

BACKGROUND

Direct mobile communications (DMC) and cellular controlled device todevice (D2D) communications are expected to play a significant role innext generation wireless networks. With DMC, the network communicates togroups of terminals or user equipments (UEs), hereafter referred to asvirtual multi-point (ViMP) nodes, instead of individual terminals.Network virtualization through terminal side cooperation (between theUEs) is expected to become part of cellular standards, such as futureversions of 3GPP LTE-A and IEEE 802.16m. A ViMP node is formed of one ormore target user equipments (TUEs) receiving/transmitting data from/tothe network and one or more cooperating UEs (CUEs) that help the TUEscommunicate with the network. Current DMC enabled systems rely on acombination of scheduling and UE grouping to enable spectrum reuse andreduce interference generated from other ViMP nodes (groups of UEs) as aresult of DMC within the ViMP nodes. The interference between ViMP nodesis referred to as inter-ViMP interference (IVI). The current systemsalso allow half-duplex UE operation but not full duplex operation mode.There is a need for an efficient scheme for DMC (or D2D) communicationsthat improves spectrum efficiency, reduce IVI, and allows a virtual fullduplex operation mode.

SUMMARY

In accordance with an embodiment, a method for supporting user equipment(UE) group based communications includes receiving, at a UE, a pluralityof data streams for a plurality of cooperating UEs (CUEs) that sharetime-domain channel resources through time-domain spreading multiplexingthat uses time-domain sparse spreading.

In another embodiment, a method for supporting UE group basedcommunications includes encoding and mapping, at a UE, a data stream,spreading the data stream over frequency-domain channel resources usingfrequency-domain spreading, and transmitting the data stream to a targetUE (TUE).

In another embodiment, a UE supporting UE group based communicationsincludes a processor and a computer readable storage medium storingprogramming for execution by the processor. The programming includinginstructions to receive a plurality of data streams for a plurality ofcooperating UEs (CUEs) that share space-domain channel resources viaspace-domain spreading multiplexing.

In yet another embodiment, a UE supporting UE group based communicationsincludes a processor and a computer readable storage medium storingprogramming for execution by the processor. The programming includesinstructions to encode and map, at a UE, a data stream, spread the datastream over at least one of frequency-domain channel resources usingfrequency-domain spreading, over time-domain channel resources usingtime-domain spreading, and over space-domain channel resources usingspace-domain spreading, and transmit the data stream to a target UE(TUE).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a scheme that combines scheduling and UE groupingaccording to current systems;

FIG. 2 illustrates a BS communicating with cooperating UEs;

FIG. 3 illustrates D2D communications with UE cooperation;

FIG. 4 illustrates an embodiment of a D2D transmission scheme usingLDS-OFDM;

FIG. 5 illustrates a embodiment scheme for two-dimensional low densityspreading (LDS) multiplexing; and

FIG. 6 illustrates a processing system that can be used to implementvarious embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

FIG. 1 illustrates a scheme 100 that is used in current wireless orcellular systems to combines scheduling and UE grouping. In existingsystems, target UEs (TUEs) for data packets in each cell are dividedinto two distinct groups. For example, the TUEs close to each other areplaced in separate groups. The D2D transmissions within ViMP nodesassociated with each group are done sequentially. The motive for thisgrouping of TUEs is to ensure that the entire spectrum is utilized allof the time, and further to reduce IVI. At each consecutive time slot orperiod, the groups switch frequency bands to transmit or receive.

FIG. 2 illustrates a scheme 200 for base station (BS) 210 communicationswith a group of cooperating UEs. UE cooperation provides diversity inspace, time and frequency. Cooperative diversity at the terminal or UEside also increases the robustness against fading and interference. Inthe scheme 200, a plurality of UEs cooperate to form one or morelogical/virtual multi-point (ViMP) nodes 230, for example in a coveragerange or cell 240 of the BS 210. A ViMP node 230 acts as a singledistributed virtual transceiver, e.g., a receiver in the downlink and atransmitter in the uplink. A ViMP node 230 may consist of a set of oneor more cooperating UEs (CUEs) 225 and a set of one or more target UEs(TUEs) 220. The CUEs 225 help the TUEs 220 communicate with the BS 210or the network, e.g., to receive data on the downlink and transmit dataon the uplink.

Downlink ViMP reception involves two stages. At a first downlinkbroadcast phase, the BS 210 or network broadcasts a data packet to theViMP receiver (Rx) node 230 using a ViMP Radio Network TemporaryIdentifier (RNTI), which is an identifier of the ViMP Rx node 230.Depending on the ViMP cooperation scenario (e.g., capacity enhancement,coverage extension, or other scenarios), both TUEs 220 and CUEs 225 maylisten to the data during this phase. At second D2D data forwardingphase, the CUEs 225 forward some information to the TUEs 220 to help theTUEs 220 decode the information broadcasted by the BS 210 or networkduring the first phase. Information sent by the CUEs 225 during thesecond phase depends on the ViMP cooperation strategy (e.g.,decode-and-forward (DF), amplify-and-forward (AF), joint reception (JR),or other strategies).

Typically, UEs in current systems can only operate in half-duplex mode,where either the UEs transmit or receive data at a time but cannottransmit and receive simultaneously. Therefore, in the context of ViMPreception, half-duplex CUEs cannot be simultaneously involved in bothdownlink reception and data forwarding phases at any given transmissiontime interval. Further, when D2D communications take place in the samefrequency band as traditional network operations, a number of issuesarise in the context of ViMP reception. For instance, the TUEs 220 mayreceive help from different CUEs 225, causing signal interference at anyof the TUEs 220. Thus, there is a need for a multi-access (ormultiplexing) scheme that enables separation at the TUEs 220 oftransmissions from a plurality of CUEs 225, without incurringsubstantial overhead cost. Another issue is that a UE may need to act asa CUE 225 and a TUE 220 simultaneously (while communicating withdifferent other UEs). Even though UEs may be limited by theirhalf-duplex capability, the UEs can act as TUEs and CUEs simultaneouslyby operating in a logical or virtual full-duplex mode. In yet anotherissue, multiple CUEs 225 may share the same frequency band for spectrumefficiency purposes. Hence, there is a need to handle, during the dataforwarding phase, the IVI interference generated or cause by the D2Dtransmissions from different ViMP nodes 230.

System and method embodiments are provided herein to achieve efficientDMC and D2D communications with improved spectrum efficiency, reducedIVI, and virtual full duplex operation mode. The embodiments include adistributed mechanism for D2D communications that enables multiple CUEsto help multiple TUEs with limited additional signaling overhead andrelatively simple implementation. The mechanism comprises a grantlesstwo-dimensional multiplexing scheme that uses low density spreading(LDS) over time, frequency and/or space domains to enable dataforwarding between multiple half-duplex terminals or UEs, e.g., within agiven frequency band, while allowing the UEs to operate in virtualfull-duplex mode.

In addition to enabling a half-duplex CUE to operate in virtualfull-duplex mode, the mechanism also allows full reuse of the spectrumfor D2D data forwarding within multiple ViMP nodes while minimizing theIVI. The signatures for the two-dimensional LDS multiplexing scheme areUE specific and can be pre-assigned or acquired based on the UEconnection ID. If the signatures are network assigned, terminals can beinformed of the assigned signature by the network through a broadcastchannel or radio resource control (RRC) signaling. The terms terminalsand UEs are used herein interchangeably to refer to any device that cancommunicate with a wireless network, e.g., via a BS. Examples of aterminal or UE include a smartphone, a desktop computer, or any othermobile or personal device enabled for wireless communications.

FIG. 3 illustrates a system 300 for D2D communications with UEcooperation. A plurality of UEs cooperate to form a logical/virtualmulti-point (ViMP) node 330 acting as single distributed virtualtransceiver. The term ViMP node is also be referred to herein as a UEgroup or a group of cooperating UEs. A ViMP node 330 includes a set oftarget UEs (TUEs) 320 and cooperating UEs (CUEs) 325. The CUEs 325 helpthe TUEs 120 communicate with a wireless network (not shown), e.g., toreceive data on the downlink and/or transmit data on the uplink. Assuch, the UEs of the ViMP node 330 can jointly transmit data on theuplink channel and jointly receive data on the downlink channel. TheTUEs 320 need to distinguish between the signals received from differentCUEs 325 during the data forwarding phase. The TUEs 320 may also act asCUEs 325 for each other. Since all D2D transmissions share the samefrequency band, there may be interference or IVI originating from D2Dtransmissions in other ViMP nodes (not shown). Close-range D2Dtransmissions can be used in order to reduce the deleterious effects ofIVI. Still, if two TUEs in different ViMP nodes are located insufficiently close proximity, then their respective ViMP nodes can causeIVI to each other.

FIG. 4 illustrates an embodiment of a D2D transmission scheme 400 usingLDS-Orthogonal frequency-division multiplexing (OFDM). The scheme 400can be implemented in the system 300 to reduce IVI. First, data streamsof a plurality of CUEs 425 (CUE_(l) to CUE_(k), where k is an integer)are spread using a low density spreading (LDS) sequence. The CUEs 425may be located in one or more ViMP nodes. The data stream of each CUE425 can be encoded and mapped at an encoder and mapper block 401, andthen spread using a corresponding LDS spreader 402. Next, the resultingLDS sequences (S₁ to S_(k)) of the CUEs 425 are multiplied by ViMP nodespecific scrambling sequences, the effect of which is to whiten the IVI(introduce white noise characteristics). The spread data stream of eachCUE 435 is scrambled using a corresponding ViMP scrambler 403 and thenmodulated using an OFDM modulator 404. The resulting scrambled sequence(S₀) for the CUEs 435 is then transmitted over the different subcarriersusing corresponding radio channel transmitters 405. The combination ofthe transmitted sequences over the air is received by a receiver of aTUE 420 within sufficient proximity, e.g., within the same ViMP node ofthe CUEs 435. The TUE 420 may also receive data corresponding to CUEs425 in other ViMP nodes of the TUE 420.

At the TUE 420, the received combination of sequences may also includeadded noise, for instance Additive white Gaussian noise (AWGN). Thereceived combination of sequences is demodulated via an OFDM demodulator406 and then descrambled at a ViMP descrambler 407 using the same ViMPscrambling sequence used in the ViMP scrambler 403 at the transmitterside. The resulting sequences are then processed by a LDS detector 408to separate the combination of sequences into individual sequencescorresponding to the different CUEs 425. For instance, the data streamsfor each virtual multi-point (ViMP) Radio node are separated accordingto a corresponding ViMP RNTI, and the data streams for each of the CUEsare separated according to a corresponding UE connection ID. Eachsequence is then decoded by a mapper and decoder 409 to obtain theoriginal data streams of the CUEs 425, e.g., of the same ViMP node orcommunicating with the TUE 420.

FIG. 5 illustrates an embodiment scheme 500 for two-dimensional LDSmultiplexing over both time and frequency grids. For instance, thescheme 500 may be used to spread the data streams of the different CUEs425 in the scheme 400 or to spread communications of the different CUEs325 and TUEs 320 in the system 300. The data streams in the streamscheme 500 are spread using LDS in both time and frequency-domains. Thedata streams share frequency-domain channel resources viafrequency-domain LDS multiplexing and share time-domain channelresources through time-domain LDS multiplexing. The time-domainspreading and the frequency-domain spreading can be independent of eachother. With respect to LDS in the time-domain, a plurality ofhalf-duplex UEs 520 can forward data to each other within the same ViMPnode, e.g., the UEs 520 simultaneously act as TUEs and CUEs. Thus, theUEs 520 need to listen and talk at the same time. However, thehalf-duplex constraint means the received signal over any subcarrierwithin a given transmission time interval (TTI) needs to be replacedwith the subcarrier's transmitted signal over the same TTI. To overcomethis, signals from TUEs are spread using LDS time-domain sequences.Specifically, transmission-off slots (zero or no transmission slots) ofthe time-domain LDS signatures are introduced to allow data reception atthose slots, thereby achieving virtual full-duplex operation in thetime-domain. Due to the LDS of the time-domain spreading, collisions inthe time-domain can be allowed and data can still be recovered at theintended receivers, for instance using iterative message passingalgorithms (MPA) with linear complexity. A TUE can apply a MPA over thetwo-dimensional time-frequency grid of the scheme 500 to recover thesignals forwarded by all CUEs within the same ViMP node.

As described above, the grantless LDS scheme over both time andfrequency grids includes a plurality of benefits. The LDS over timeallows virtual full-duplex operation, thereby overcoming the half-duplexUE constraint. Further, the LDS over frequency acts as a channelizationcode to allow multiple CUEs to share the same frequency band with noadditional signaling overhead. The signatures are UE specific and can bepre-assigned or acquired based on a UE connection ID. Additionally, aViMP-specific scrambling code is used which allows whitening the effectsof IVI, thereby allowing D2D communications for different UEs to sharethe same frequency band without causing substantial interference. Theembodiments herein may be implemented in, for example, any wirelesscellular network with D2D enhanced capability including but not limitedto 3GPP LTE, LTE-A and IEEE WiMAX for instance.

FIG. 6 is a block diagram of a processing system 600 that can be used toimplement various embodiments. Specific devices may utilize all of thecomponents shown, or only a subset of the components, and levels ofintegration may vary from device to device. Furthermore, a device maycontain multiple instances of a component, such as multiple processingunits, processors, memories, transmitters, receivers, etc. Theprocessing system 600 may comprise a processing unit 601 equipped withone or more input/output devices, such as a speaker, microphone, mouse,touchscreen, keypad, keyboard, printer, display, and the like. Theprocessing unit 601 may include a central processing unit (CPU) 610, amemory 620, a mass storage device 630, a video adapter 640, and an I/0interface 665 connected to a bus. The bus may be one or more of any typeof several bus architectures including a memory bus or memorycontroller, a peripheral bus, a video bus, or the like.

The CPU 610 may comprise any type of electronic data processor. Thememory 620 may comprise any type of system memory such as static randomaccess memory (SRAM), dynamic random access memory (DRAM), synchronousDRAM (SDRAM), read-only memory (ROM), a combination thereof, or thelike. In an embodiment, the memory 620 may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms. The mass storage device 630 may comprise any type of storagedevice configured to store data, programs, and other information and tomake the data, programs, and other information accessible via the bus.The mass storage device 630 may comprise, for example, one or more of asolid state drive, hard disk drive, a magnetic disk drive, an opticaldisk drive, or the like.

The video adapter 640 and the I/0 interface 665 provide interfaces tocouple external input and output devices to the processing unit. Asillustrated, examples of input and output devices include a display 660coupled to the video adapter 640 and any combination ofmouse/keyboard/printer 670 coupled to the I/0 interface 665. Otherdevices may be coupled to the processing unit 601, and additional orfewer interface cards may be utilized. For example, a serial interfacecard (not shown) may be used to provide a serial interface for aprinter.

The processing unit 601 also includes one or more network interfaces650, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or one or more networks 680.The network interface 650 allows the processing unit 601 to communicatewith remote units via the networks 680. For example, the networkinterface 650 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing unit 601 is coupled to alocal-area network or a wide-area network for data processing andcommunications with remote devices, such as other processing units, theInternet, remote storage facilities, or the like.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method for supporting user equipment (UE) groupbased communications, comprising: receiving, at a UE, a plurality ofdata streams from a plurality of cooperating UEs (CUEs) that share timedomain channel resources, the plurality of data streams beingtime-domain multiplexed using time-domain sequences.
 2. The method ofclaim 1, further comprising: transmitting, at the UE, a data stream toat least one of the plurality of CUEs, wherein the UE and the pluralityof CUEs share time domain channel resources.
 3. The method of claim 2,the plurality of data streams being frequency-domain multiplexed usingfrequency-domain sequences.
 4. The method of claim 3, the plurality ofdata streams being time-domain multiplexed independently from theplurality of data streams being frequency-domain multiplexed.
 5. Themethod of claim 3, wherein the UE is configured for half-duplexoperations, and the frequency-domain sequences enable the UE for virtualfull-duplex operations.
 6. The method of claim 1, wherein the UE isconfigured for half-duplex operations, and the time-domain sequencesenable the UE for virtual full-duplex operations.
 7. The method of claim1, further comprising: separating, via a multi-data-stream detector,descrambled plurality of data streams for each UE group according to acorresponding UE group Network Temporary Identifier (RNTI) and for eachof the CUEs according to a corresponding UE connection ID for assigningUE-specific sequences.
 8. The method of claim 1, further comprisingidentifying each of the plurality of data streams according toUE-specific sequences of the CUEs.
 9. The method of claim 1, furthercomprising determining at the UE on periods or off periods based on thetime-domain sequences, wherein: during the on periods, the UE transmitsdata, and during the off periods, the UE listens or receives data.
 10. Auser equipment (UE) supporting UE group based communications, the UEcomprising: a processor; and a computer readable storage medium storingprogramming for execution by the processor, the programming includinginstructions to receive a plurality of data streams from a plurality ofcooperating UEs (CUEs) that share time domain channel resources, theplurality of data streams being time-domain multiplexed usingtime-domain sequences.
 11. The UE of claim 10, the programming includingfurther instructions to: transmit a data stream to at least one of theplurality of CUEs, wherein the UE and the plurality of CUEs share timedomain channel resources.
 12. The UE of claim 11, the plurality of datastreams being frequency-domain multiplexed using frequency-domainsequences.
 13. The UE of claim 12, the plurality of data streams beingtime-domain multiplexed independently from the plurality of data streamsbeing frequency-domain multiplexed.
 14. The UE of claim 12, wherein theUE is configured for half-duplex operations, and the frequency-domainsequences enable the UE for virtual full-duplex operations.
 15. The UEof claim 10, wherein the UE is configured for half-duplex operations,and the time-domain sequences enable the UE for virtual full-duplexoperations.
 16. The UE of claim 10, the programming including furtherinstructions to: separate, via a multi-data-stream detector, descrambledplurality of data streams for each UE group according to a correspondingUE group Network Temporary Identifier (RNTI) and for each of the CUEsaccording to a corresponding UE connection ID for assigning UE-specificsequences.
 17. The UE of claim 10, the programming including furtherinstructions to identify each of the plurality of data streams accordingto UE-specific sequences of the CUEs.
 18. The UE of claim 10, theprogramming including further instructions to determine on periods oroff periods based on the time-domain sequences, wherein: during the onperiods, the UE transmits data, and during the off periods, the UElistens or receives data.
 19. A method for supporting user equipment(UE) group based communications, comprising: transmitting, at a firstcooperating UE (CUE), a first data stream to at least one of a pluralityof target UEs, the first data stream being time-domain multiplexed withat least one of a first plurality of data streams from at least one of aplurality of CUEs using time-domain sequences, wherein the first CUEshare the time domain channel resources with the at least one of theplurality of CUEs.
 20. The method of claim 19, further comprising:receiving, at the first CUE, at least one of a second plurality of datastreams from at least one of the plurality of CUEs.
 21. The method ofclaim 19, wherein the plurality of CUEs use sequences from a pool ofradio resource control (RRC) configured UE-specific sequences fortime-domain multiplexing the plurality of data streams.
 22. Acooperating user equipment (CUE) supporting user equipment (UE) groupbased communications, the UE comprising: a processor; and a computerreadable storage medium storing programming for execution by theprocessor, the programming including instructions to transmit a firstdata stream to at least one of a plurality of target UEs, the first datastream being time-domain multiplexed with at least one of a firstplurality of data streams from at least one of a plurality of CUEs usingtime-domain sequences, wherein the CUE share the time domain channelresources with the at least one of the plurality of CUEs.
 23. The CUE ofclaim 22, the programming including further instructions: receive atleast one of a second plurality of data streams from at least one of theplurality of CUEs.
 24. The CUE of claim 22, wherein the plurality ofCUEs use sequences from a pool of radio resource control (RRC)configured UE-specific sequences for time-domain multiplexing theplurality of data streams.